As conventionally known, an internal combustion engine is equipped with an ignition device (e.g., an ignition plug), which includes a central electrode (i.e., an ignition electrode), insulated and held by an insulator and paired with a confronting ground electrode, and is configured to generate a spark in response to a voltage applied between the central electrode and the ground electrode.
According to a conventional technique, if a secondary current value is lower than a predetermined threshold during a predetermined period of time since the start of spark discharging, it is determined that there has occurred a phenomenon that the flow of an air-fuel mixture extinguishes the spark discharge (hereinafter, referred to as “spark discharge blow-out phenomenon”), and supplementary spark discharging is continuously performed after the main discharge in the next cycle. In this case, it is said that setting the secondary current value to be a value obtainable by adding a predetermined current value to the predetermined threshold can prevent the spark discharge blow-out phenomenon from arising in the next cycle.
However, the above-mentioned conventional technique requires obtaining a current value at which the spark discharge is blown out in the previous cycle and setting the obtained value as a discharge current value in the next cycle. Accordingly, performing spark discharging without any current control is required in the previous cycle. Further, predicting whether the spark discharge is blown out is substantially difficult and therefore an unintended spark discharge blow-out phenomenon may easily arise.